This invention relates to laminated elastic composites that are suitable for use in tapes, wraps and bandages, and to a method of making such laminated elastic composites.
Elastic composite materials are widely used in many forms in a large number of medical products such as tapes, wraps, bandages and wound dressings. Elastic medical products offer many advantages over non-elastic products. Elastic materials are highly conformable to body contours and serve a therapeutic purpose by applying necessary, elastically-resilient pressure over an injured or wounded area during the period that the bandage is in place. In addition, due to the elasticity in such products, they are commonly used to gently and safely immobilize wounded limbs, such as sprained ankles, without resorting to more expensive and restrictive casting methods.
Elastic bandages should preferably be absorbent so that blood and wound exudate may be removed from direct contact with a wound while it is being treated. They should also be breathable to allow for the transpiration of water vapor and other gases. In addition, they should be soft to the touch and conformable in that they readily conform to the contours of irregular surfaces such as parts of the body without crinkling, creasing or cracking. They should also be strong and have a high tensile strength. It is also desirable that elastic bandages be inexpensive and that they be made with economical materials and efficient processes.
Although all of these properties are pursued by workers in the field, it is difficult in practice to produce a single elastic composite that possesses them all, because the materials and methods that are ideally suited to provide some of the desired properties may at the same time possess countervailing qualities that prevent the achievement of others. For example, some polymeric films possess the desirable properties of strength and low cost of manufacture, yet these same films have the disadvantage of being neither breathable nor conformable.
Elastic composites are known that incorporate one or more nonwoven fiber webs as components. U.S. Pat. No. 4,984,584 describes a shirred cohesive bandage that includes two nonwoven fiber web outer layers and an inner layer of substantially parallel elastic yarns oriented in the machine direction. The fabric of the bandage is made by advancing a layer of stretched elastic yarns into a double roller apparatus, which simultaneously sandwiches the elastic yarns between two nonwoven carded webs and coats the resulting composite with a binder material. The composite is then passed through a drying oven and collected on a roll.
Elastic composites are also made by combining elastic and nonelastic nonwoven webs. For instance, U.S. Pat. No. 4,863,779 describes an elastic composite comprising an elastic nonwoven fiber web thermally bonded to one or more nonelastic nonwoven fiber webs.
U.S. Pat. No. 5,385,775 describes an elastic composite that includes two outer nonwoven fiber webs and an inner elastic fibrous web. The elastic fibrous web is said to comprise one layer of elastomeric melt blown fibers and one layer of parallel elastomeric filaments. The composite is made by advancing a stretched elastic nonwoven fiber web into the heated nip of a double roller apparatus where it is sandwiched between the nonwoven fiber webs and thermally bonded.
Elastic composites may also be formed by melt blowing fibers onto elastic filaments or pre-made fiber webs. U.S. Pat. No. 5,219,633 (the ""633 patent) describes an elastic composite that is formed in-line by extruding elastic filaments into parallel rows and then melt blowing fibers onto the elastic filaments. The two layers are then squeezed between opposing heated rollers to form a nonwoven-elastic composite. The melt blown fibers may be adhesive or pressure-sensitive adhesive fibers. Nonwoven cover webs may also be provided as additional layers in the composite. The ""633 patent also discloses a method of making an elastic composite in which fibers are melt blown between two non-woven layers at the nip of a thermally bonding apparatus. The composite also includes a layer of elastic filaments, which may be extruded at the nip as well.
The invention provides laminated elastic composites that include an elastic layer and a layer of fibers that are melt blown onto the elastic layer in an in-line process. The elastic layer includes a layer of substantially parallel, spaced apart elastic filaments oriented in the machine direction.
In one embodiment of the invention, the laminate composite includes a nonwoven fiber cover web and has a configuration generally represented as nonwoven//elastic//melt blown fiber.
In yet another embodiment, a second nonwoven cover web is provided, and the laminate composite has a configuration generally represented as first nonwoven//elastic//melt blown fiber//second nonwoven.
The invention also provides embodiments in which a scrim layer is included as a layer in the laminate composite.
The invention also provides a method of making elastic laminate composites. The method of the invention is practiced with an apparatus that includes a melt blowing die, a collector drum, a roll upstream from the die for dispensing a continuous length of a first nonwoven fiber web, a roll for dispensing a layer of substantially parallel elastomeric fibers upstream from the die, a roll for dispensing a second nonwoven web downstream from the die, a calender roll that forms a nip with the collector drum for thermally bonding the composite, and a winder roll for collecting the elastic composite after thermal bonding is complete.
To form an elastic composite using this apparatus, the first nonwoven fiber web and the elastic layer are dispensed from the upstream rolls and advanced over the collector drum in such a manner that the elastic filaments are situated between the nonwoven material and the die. These two layers are advanced forward and the melt blowing die deposits a layer of melt blown adhesive fibers on the elastic layer, binding together the elastic filaments to the nonwoven web and to the melt blown layer. The three layers are then advanced toward the nip formed by the collector drum and the squeezing roll. The second nonwoven fiber web is brought into contact with the exposed surface of the melt blown adhesive fibers and the composite is pressure laminated bonded as it advances through the opposing temperature controlled rollers. The elastic layer is stretched substantially beyond its relaxed state before and during lamination of the nonwoven fiber webs and scrim to the elastic layer (e.g., the elastic layer is stretched in the machine direction at least 50 percent beyond its relaxed state, and preferably 50-300%). The composite fabric is then relaxed and collected onto the winder roll.
The elastic composite made by this method comprises a first nonwoven fiber layer, an elastic layer comprising substantially parallel elastomeric filaments, a melt blown fiber adhesive layer and a second nonwoven fiber layer.
Several alternative elastic composites can be made within the method of the invention. The apparatus may be modified to include an upstream roll for dispensing a scrim that comprises spaced-apart filaments oriented in the machine direction that are substantially perpendicular to spaced-apart filaments oriented in the cross direction. Using this modified apparatus, a length of scrim material may be placed between the first nonwoven web and the elastic layer of the elastic composite. The presence of the scrim in this composite provides added tensile strength to the composite and provides the advantage of facilitating tearing in either the machine direction or the cross direction along the lines provided by the filaments.
In another alternative, the nonwoven rolls are eliminated, and the adhesive fibers are melt blown onto the elastic layer to form a composite that comprises an elastic layer comprising substantially parallel elastomeric filaments and melt blown adhesive fibers. This method may be further modified to provide a scrim layer so that the resulting composite comprises a scrim layer, an elastic layer comprising substantially parallel elastomeric filaments and a melt blown adhesive fiber layer.
The nonwoven webs and scrim of the laminated elastomeric composite also form loops useful as part of a hook and loop fastening system, and are well adapted for use with the hook system described, for example, in U.S. patent application Ser. No. 09/257,447, filed Feb. 25, 1999 now abandoned.